¹essential

essential, fundamental, vital, cardinal mean so important as to be indispensable. essential implies belonging to the very nature of a thing and therefore being incapable of removal without destroying the thing itself or its character <conflict is essential in drama>. fundamental applies to something that is a foundation without which an entire system or complex whole would collapse <fundamental principles of algebra>. vital suggests something that is necessary to a thing's continued existence or operation <cut off from vital supplies>. cardinal suggests something on which an outcome turns or depends <a cardinal rule in buying a home>.